The term "multifilament thread" or "multifilament" covers threads which are built up from many single so-called filaments. Those manufactured from plastics material form the starting form for industrial yarns, sewing yarns, yarns for belts, ropes or similar. Thermoplastic materials such as polypropylene, polyethylene, polyester or polyamides such as e.g. nylon are used.
One process for manufacturing a multifilament thread is described for example in the EP 0 726 338 A2. Such apparatus consist of an extruder in which granules of the starting material are melted and pressed through a spinning nozzle. Depending on the intended use, a specific number of filaments is combined into a thread and drawn off from the extruder via a system of deflector rollers. The spun thread is subsequently drawn to increase its strength. This is carried out by heated rollers rotating at different speeds. The drawing ratio is determined by the ratio of the speed of the rollers. To be able to transfer sufficient heat to the thread, the thread loops several times round a pair of rollers, a so-called "galette pair", and is then fed to a further pair of rollers. The rollers of a galette pair must have exactly equal speeds. If the final desired drawing ratio is reached, the thread is finally wound onto a bobbin roller. After this, it is processed further according to its intended use. Thus, the thread can be given an appropriate character by subsequent texturizing.
To draw the thread further, in particular for high-strength threads, it also passes through hot air modules or ovens in which the thread is heated to very high temperatures by an air blower, and is again drawn through rollers rotating at different speeds before and after the oven. In addition, such ovens can be used as a relaxation stage, whereby the thread is stabilized and has a relatively high elasticity and a low residual shrinkage. Such yarns are used for example for the manufacture of base layers for carpets where strength is less important, but the elasticity of the yarn is certainly a factor. To prevent the carpet from bulging subsequently, the carpet base must not have a high residual shrinkage.